The present invention relates to plate-type heat exchangers, particularly heat exchangers for conveying polluted gases having solid materials entrained therein, and more specifically to a jet cleaning apparatus for use in conjunction with such heat exchangers.
Plate-type heat exchangers are well-known in the art, usually comprising a rectangular housing having a plurality of parallel, spaced-apart plates enclosed therein, opposite ends of parallel pairs of such plates along one axis being sealed together to form parallel flow channels, opposite ends of intermediate plates along a normal axis being sealed together to provide transverse flow channels through the intermediate end plates. Such devices typically provide a flow path through the plurality of channels for conveying heated and usually polluted gases, and consequent transverse paths through the intermediate channels for conveying a cooling gas, which cooling gas absorbs heat through contact with the plates, and emerges from the heat exchanger warmed to an elevated temperature, which heated gas may be reused in industrial processes. In such devices the parallel channels which convey the dirty gas tend to accumulate pollutants over time, the pollutants adhering to the walls and interior surfaces of the channels, thereby reducing the heat transfer efficiency of the apparatus and eventually clogging the free flow of gas therethrough. Frequently, clogged channels become the focus of heat build-up within the heat exchanger, which heat build-up can combine with the pollutants to corrode the heat exchanger material and eventually cause openings to erode into the clean gas channels, thereby destroying the effectiveness of the heat exchanger.
Various mechanical, liquid and pneumatic devices have been used in the past to clean the flow channels of such heat exchangers, for it has long been established that it is necessary to periodically clean these channels in order to maintain the efficiency of operation of the heat exchanger. Of course, it is always possible to shut down the entire system so that the interior channels of the heat exchanger may be scrubbed down and washed out with cleaning liquids. Various mechanical cleaning mechanisms, including chain devices, moving arms, etc. have been used to either scrape the interior surfaces of the flow channels or to develop mechanical shock impact against the channels to vibrate pollutants free from adherence to the channels. Air jet blasts have been used to attempt to blow pollutants free of the channels, and one such device is disclosed in U.S. Pat. No. 4,366,003, issued Dec. 28, 1982. In this device, individual air jets are positioned over the respective inlets of a plurality of pipes, each pipe comprising a heat exchanger pipe through which heated pollutant material flows. The air jets are formed in air pressure lines, and are selectively controllable by valves intermediate the air jets and the pressure lines to sequentially actuate a jet of air into each of the tubes to develop a short term blast of air for propagating down the tubes to remove accumulated pollutants. This device requires relatively complex air valving intermediate the pressure jet openings and the air pressure lines, and although it is suitable for cleaning relatively small diameter pipes, it is not suitable for cleaning plate-type heat exchanger channels because of the limited amount of air volume available for propagating the jets, and because the number of jets are too limited for effective cleaning of an entire channel member.
It is desirable, however, to utilize the principle of air jet blast cleaning in combination with plate-type heat exchangers, for they do provide obvious advantages over mechanical and liquid cleaning systems. Accordingly, the present invention addresses the problem of constructing an air jet wave system which has the requisite operating characteristics to effectively develop a cleaning jet blast sufficient to traverse the entire length of a flow channel constructed between parallel plates in this type of heat exchanger.